Provided by: bash_4.3-6ubuntu1_amd64 bug

NAME

       bash-builtins - bash built-in commands, see bash(1)

SYNOPSIS

       bash  defines  the  following built-in commands: :, ., [, alias, bg, bind, break, builtin,
       case, cd, command, compgen, complete, continue, declare, dirs, disown, echo, enable, eval,
       exec,  exit,  export,  fc,  fg,  getopts, hash, help, history, if, jobs, kill, let, local,
       logout, popd, printf, pushd, pwd, read,  readonly,  return,  set,  shift,  shopt,  source,
       suspend,  test,  times,  trap,  type, typeset, ulimit, umask, unalias, unset, until, wait,
       while.

BASH BUILTIN COMMANDS

       Unless otherwise noted, each builtin command  documented  in  this  section  as  accepting
       options  preceded  by - accepts -- to signify the end of the options.  The :, true, false,
       and test builtins do not accept options and do not treat -- specially.  The exit,  logout,
       break,  continue,  let,  and  shift builtins accept and process arguments beginning with -
       without requiring --.  Other builtins that accept  arguments  but  are  not  specified  as
       accepting  options  interpret arguments beginning with - as invalid options and require --
       to prevent this interpretation.
       : [arguments]
              No effect; the command does nothing beyond expanding arguments and  performing  any
              specified redirections.  A zero exit code is returned.

        .  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename in the current shell environment and return
              the exit status of the last command executed from filename.  If filename  does  not
              contain  a  slash,  filenames  in  PATH  are  used to find the directory containing
              filename.  The file searched for in PATH need not be executable.  When bash is  not
              in  posix  mode, the current directory is searched if no file is found in PATH.  If
              the sourcepath option to the shopt builtin command is turned off, the PATH  is  not
              searched.   If  any  arguments  are supplied, they become the positional parameters
              when filename is executed.  Otherwise the positional parameters are unchanged.  The
              return  status  is the status of the last command exited within the script (0 if no
              commands are executed), and false if filename is not found or cannot be read.

       alias [-p] [name[=value] ...]
              Alias with no arguments or with the -p option prints the list  of  aliases  in  the
              form alias name=value on standard output.  When arguments are supplied, an alias is
              defined for each name whose value is given.  A trailing space in  value causes  the
              next  word  to  be  checked for alias substitution when the alias is expanded.  For
              each name in the argument list for which no value is supplied, the name  and  value
              of  the  alias  is printed.  Alias returns true unless a name is given for which no
              alias has been defined.

       bg [jobspec ...]
              Resume each suspended job jobspec in the background, as if it had been started with
              &.   If  jobspec is not present, the shell's notion of the current job is used.  bg
              jobspec returns 0 unless run when job control is disabled or,  when  run  with  job
              control  enabled,  any  specified  jobspec was not found or was started without job
              control.

       bind [-m keymap] [-lpsvPSVX]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind readline-command
              Display current readline key and function  bindings,  bind  a  key  sequence  to  a
              readline  function  or macro, or set a readline variable.  Each non-option argument
              is a command as it would appear in .inputrc, but each binding or  command  must  be
              passed  as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'.  Options, if
              supplied, have the following meanings:
              -m keymap
                     Use keymap as  the  keymap  to  be  affected  by  the  subsequent  bindings.
                     Acceptable  keymap  names are emacs, emacs-standard, emacs-meta, emacs-ctlx,
                     vi, vi-move, vi-command, and vi-insert.  vi  is  equivalent  to  vi-command;
                     emacs is equivalent to emacs-standard.
              -l     List the names of all readline functions.
              -p     Display  readline function names and bindings in such a way that they can be
                     re-read.
              -P     List current readline function names and bindings.
              -s     Display readline key sequences bound to macros and the strings  they  output
                     in such a way that they can be re-read.
              -S     Display readline key sequences bound to macros and the strings they output.
              -v     Display  readline  variable  names and values in such a way that they can be
                     re-read.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq:shell-command
                     Cause shell-command  to  be  executed  whenever  keyseq  is  entered.   When
                     shell-command  is executed, the shell sets the READLINE_LINE variable to the
                     contents of the readline line buffer and the READLINE_POINT variable to  the
                     current  location  of  the insertion point.  If the executed command changes
                     the value of READLINE_LINE or  READLINE_POINT,  those  new  values  will  be
                     reflected in the editing state.
              -X     List  all  key sequences bound to shell commands and the associated commands
                     in a format that can be reused as input.

              The return value is 0 unless an unrecognized option is given or an error occurred.

       break [n]
              Exit from within a for, while, until, or select loop.  If n is specified,  break  n
              levels.   n  must  be ≥ 1.  If n is greater than the number of enclosing loops, all
              enclosing loops are exited.  The return value is 0 unless n is not greater than  or
              equal to 1.

       builtin shell-builtin [arguments]
              Execute  the  specified  shell  builtin,  passing it arguments, and return its exit
              status.  This is useful when defining a function whose name is the same as a  shell
              builtin,  retaining  the  functionality of the builtin within the function.  The cd
              builtin  is  commonly  redefined  this  way.   The  return  status  is   false   if
              shell-builtin is not a shell builtin command.

       caller [expr]
              Returns  the  context  of  any active subroutine call (a shell function or a script
              executed with the . or source builtins).  Without expr, caller  displays  the  line
              number  and  source  filename  of  the  current subroutine call.  If a non-negative
              integer is supplied as expr, caller displays the line number, subroutine name,  and
              source  file  corresponding  to  that position in the current execution call stack.
              This extra information may be used, for example,  to  print  a  stack  trace.   The
              current  frame is frame 0.  The return value is 0 unless the shell is not executing
              a subroutine call or expr does not correspond to  a  valid  position  in  the  call
              stack.

       cd [-L|[-P [-e]] [-@]] [dir]
              Change the current directory to dir.  if dir is not supplied, the value of the HOME
              shell variable is the default.  Any additional arguments following dir are ignored.
              The  variable CDPATH defines the search path for the directory containing dir: each
              directory name in CDPATH is searched  for  dir.   Alternative  directory  names  in
              CDPATH  are  separated by a colon (:).  A null directory name in CDPATH is the same
              as the current directory, i.e., ``.''.  If dir begins with a slash (/), then CDPATH
              is  not  used.  The  -P option causes cd to use the physical directory structure by
              resolving symbolic links while traversing dir and before processing instances of ..
              in  dir  (see  also the -P option to the set builtin command); the -L option forces
              symbolic links to be followed by resolving the link after processing  instances  of
              ..  in  dir.   If  ..  appears  in dir, it is processed by removing the immediately
              previous pathname component from dir, back to a slash or the beginning of dir.   If
              the  -e  option  is  supplied  with -P, and the current working directory cannot be
              successfully determined after a successful directory  change,  cd  will  return  an
              unsuccessful  status.   On  systems  that  support  it,  the -@ option presents the
              extended attributes associated with a file as a directory.  An  argument  of  -  is
              converted  to  $OLDPWD  before  the  directory change is attempted.  If a non-empty
              directory name from CDPATH is used,  or  if  -  is  the  first  argument,  and  the
              directory  change is successful, the absolute pathname of the new working directory
              is written to the standard output.  The return value is true if the  directory  was
              successfully changed; false otherwise.

       command [-pVv] command [arg ...]
              Run  command  with  args suppressing the normal shell function lookup. Only builtin
              commands or commands found in the PATH are executed.  If the -p  option  is  given,
              the  search  for  command  is  performed  using  a  default  value for PATH that is
              guaranteed to find all of the standard utilities.  If either the -V or -v option is
              supplied,  a description of command is printed.  The -v option causes a single word
              indicating the command or filename used to invoke command to be displayed;  the  -V
              option  produces  a  more verbose description.  If the -V or -v option is supplied,
              the exit status is 0 if command was found, and 1 if  not.   If  neither  option  is
              supplied  and an error occurred or command cannot be found, the exit status is 127.
              Otherwise, the exit status of the command builtin is the exit status of command.

       compgen [option] [word]
              Generate possible completion matches for word according to the options,  which  may
              be any option accepted by the complete builtin with the exception of -p and -r, and
              write the matches to the standard output.  When using the -F  or  -C  options,  the
              various  shell  variables  set  by  the  programmable  completion facilities, while
              available, will not have useful values.

              The matches will be generated in the same way as  if  the  programmable  completion
              code  had  generated  them  directly  from a completion specification with the same
              flags.  If word  is  specified,  only  those  completions  matching  word  will  be
              displayed.

              The  return  value is true unless an invalid option is supplied, or no matches were
              generated.

       complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G globpat] [-W wordlist] [-F
       function] [-C command]
              [-X filterpat] [-P prefix] [-S suffix] name [name ...]
       complete -pr [-DE] [name ...]
              Specify  how  arguments  to  each  name  should  be completed.  If the -p option is
              supplied, or if no options are supplied,  existing  completion  specifications  are
              printed  in  a way that allows them to be reused as input.  The -r option removes a
              completion specification  for  each  name,  or,  if  no  names  are  supplied,  all
              completion  specifications.  The -D option indicates that the remaining options and
              actions should apply to the ``default'' command  completion;  that  is,  completion
              attempted on a command for which no completion has previously been defined.  The -E
              option indicates that the remaining options and actions should apply  to  ``empty''
              command completion; that is, completion attempted on a blank line.

              The  process  of  applying  these completion specifications when word completion is
              attempted is described above under Programmable Completion.

              Other options, if specified, have the following meanings.  The arguments to the -G,
              -W,  and  -X options (and, if necessary, the -P and -S options) should be quoted to
              protect them from expansion before the complete builtin is invoked.
              -o comp-option
                      The comp-option controls several aspects of the compspec's behavior  beyond
                      the simple generation of completions.  comp-option may be one of:
                      bashdefault
                              Perform  the  rest  of the default bash completions if the compspec
                              generates no matches.
                      default Use  readline's  default  filename  completion  if   the   compspec
                              generates no matches.
                      dirnames
                              Perform  directory  name  completion  if  the compspec generates no
                              matches.
                      filenames
                              Tell readline that the compspec  generates  filenames,  so  it  can
                              perform  any  filename-specific  processing (like adding a slash to
                              directory  names,  quoting  special  characters,   or   suppressing
                              trailing spaces).  Intended to be used with shell functions.
                      noquote Tell  readline  not  to  quote  the  completed  words  if  they are
                              filenames (quoting filenames is the default).
                      nospace Tell readline  not  to  append  a  space  (the  default)  to  words
                              completed at the end of the line.
                      plusdirs
                              After  any matches defined by the compspec are generated, directory
                              name completion is attempted and  any  matches  are  added  to  the
                              results of the other actions.
              -A action
                      The  action  may  be  one  of  the following to generate a list of possible
                      completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.  May also be specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also be specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames, as taken from the file specified by the  HOSTFILE  shell
                              variable.
                      job     Job names, if job control is active.  May also be specified as -j.
                      keyword Shell reserved words.  May also be specified as -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o option to the set builtin.
                      shopt   Shell option names as accepted by the shopt builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be specified as -v.
              -C command
                      command  is  executed  in a subshell environment, and its output is used as
                      the possible completions.
              -F function
                      The shell function function is executed in the current  shell  environment.
                      When  the  function is executed, the first argument ($1) is the name of the
                      command whose arguments are being completed, the second  argument  ($2)  is
                      the word being completed, and the third argument ($3) is the word preceding
                      the word being completed on the current command line.   When  it  finishes,
                      the  possible  completions  are  retrieved  from the value of the COMPREPLY
                      array variable.
              -G globpat
                      The pathname expansion pattern globpat is expanded to generate the possible
                      completions.
              -P prefix
                      prefix  is  added  at  the  beginning of each possible completion after all
                      other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all other options have
                      been applied.
              -W wordlist
                      The  wordlist  is split using the characters in the IFS special variable as
                      delimiters, and each resultant word is expanded.  The possible  completions
                      are the members of the resultant list which match the word being completed.
              -X filterpat
                      filterpat  is  a  pattern as used for pathname expansion.  It is applied to
                      the list of possible completions generated by  the  preceding  options  and
                      arguments, and each completion matching filterpat is removed from the list.
                      A leading ! in filterpat negates the pattern; in this case, any  completion
                      not matching filterpat is removed.

              The return value is true unless an invalid option is supplied, an option other than
              -p or -r is supplied without a name argument,  an  attempt  is  made  to  remove  a
              completion  specification for a name for which no specification exists, or an error
              occurs adding a completion specification.

       compopt [-o option] [-DE] [+o option] [name]
              Modify completion options for each name  according  to  the  options,  or  for  the
              currently-executing  completion if no names are supplied.  If no options are given,
              display the completion options for  each  name  or  the  current  completion.   The
              possible values of option are those valid for the complete builtin described above.
              The -D option indicates that the remaining options should apply to the  ``default''
              command  completion;  that  is,  completion  attempted  on  a  command for which no
              completion has previously been defined.  The -E option indicates that the remaining
              options should apply to ``empty'' command completion; that is, completion attempted
              on a blank line.

              The return value is true unless an invalid option is supplied, an attempt  is  made
              to  modify  the options for a name for which no completion specification exists, or
              an output error occurs.

       continue [n]
              Resume the next iteration of the enclosing for, while, until, or select loop.  If n
              is  specified,  resume  at the nth enclosing loop.  n must be ≥ 1.  If n is greater
              than the number of enclosing loops, the  last  enclosing  loop  (the  ``top-level''
              loop)  is  resumed.  The return value is 0 unless n is not greater than or equal to
              1.

       declare [-aAfFgilnrtux] [-p] [name[=value] ...]
       typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
              Declare variables and/or give them attributes.  If no names are given then  display
              the  values  of variables.  The -p option will display the attributes and values of
              each name.  When -p is used with name arguments, additional options, other than  -f
              and  -F,  are ignored.  When -p is supplied without name arguments, it will display
              the attributes and values of all variables having the attributes specified  by  the
              additional options.  If no other options are supplied with -p, declare will display
              the attributes and values of all shell variables.  The -f option will restrict  the
              display  to  shell  functions.   The  -F  option  inhibits  the display of function
              definitions; only the function name and attributes are printed.   If  the  extdebug
              shell option is enabled using shopt, the source file name and line number where the
              function is defined are displayed as well.  The  -F  option  implies  -f.   The  -g
              option  forces  variables  to be created or modified at the global scope, even when
              declare is executed in a shell function.  It is ignored in all  other  cases.   The
              following  options  can  be used to restrict output to variables with the specified
              attribute or to give variables attributes:
              -a     Each name is an indexed array variable (see Arrays above).
              -A     Each name is an associative array variable (see Arrays above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC
                     EVALUATION above) is performed when the variable is assigned a value.
              -l     When  the  variable  is  assigned  a  value,  all  upper-case characters are
                     converted to lower-case.  The upper-case attribute is disabled.
              -n     Give each name the nameref attribute, making it a name reference to  another
                     variable.   That  other  variable  is  defined  by  the  value of name.  All
                     references and assignments to name, except for  changing  the  -n  attribute
                     itself,  are  performed  on the variable referenced by name's value.  The -n
                     attribute cannot be applied to array variables.
              -r     Make names  readonly.   These  names  cannot  then  be  assigned  values  by
                     subsequent assignment statements or unset.
              -t     Give  each name the trace attribute.  Traced functions inherit the DEBUG and
                     RETURN traps from the calling shell.  The trace  attribute  has  no  special
                     meaning for variables.
              -u     When  the  variable  is  assigned  a  value,  all  lower-case characters are
                     converted to upper-case.  The lower-case attribute is disabled.
              -x     Mark names for export to subsequent commands via the environment.

              Using `+' instead of `-' turns off the attribute instead, with the exceptions  that
              +a may not be used to destroy an array variable and +r will not remove the readonly
              attribute.  When used in a function, declare and typeset make each name  local,  as
              with  the  local  command, unless the -g option is supplied.  If a variable name is
              followed by =value, the value of the variable is set to value.  When using -a or -A
              and the compound assignment syntax to create array variables, additional attributes
              do not take effect until subsequent assignments.  The return value is 0  unless  an
              invalid  option  is encountered, an attempt is made to define a function using ``-f
              foo=bar'', an attempt is made to assign a value to a readonly variable, an  attempt
              is  made  to  assign  a  value  to  an  array  variable  without using the compound
              assignment syntax (see Arrays above), one  of  the  names  is  not  a  valid  shell
              variable  name,  an  attempt  is  made  to  turn off readonly status for a readonly
              variable, an attempt is made to turn off array status for an array variable, or  an
              attempt is made to display a non-existent function with -f.

       dirs [-clpv] [+n] [-n]
              Without  options,  displays  the  list  of  currently  remembered directories.  The
              default display is on a single line  with  directory  names  separated  by  spaces.
              Directories  are added to the list with the pushd command; the popd command removes
              entries from the list.
              -c     Clears the directory stack by deleting all of the entries.
              -l     Produces a listing using full pathnames; the default listing format  uses  a
                     tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print the directory stack with one entry per line, prefixing each entry with
                     its index in the stack.
              +n     Displays the nth entry counting from the left of the list shown by dirs when
                     invoked without options, starting with zero.
              -n     Displays  the  nth  entry  counting from the right of the list shown by dirs
                     when invoked without options, starting with zero.

              The return value is 0 unless an invalid option is supplied or n indexes beyond  the
              end of the directory stack.

       disown [-ar] [-h] [jobspec ...]
              Without  options, remove each jobspec from the table of active jobs.  If jobspec is
              not present, and neither the -a nor the -r option is supplied, the current  job  is
              used.   If  the -h option is given, each jobspec is not removed from the table, but
              is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP.  If
              no  jobspec  is  supplied,  the  -a option means to remove or mark all jobs; the -r
              option without a jobspec argument restricts operation to running jobs.  The  return
              value is 0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output  the args, separated by spaces, followed by a newline.  The return status is
              0 unless a write error occurs.   If  -n  is  specified,  the  trailing  newline  is
              suppressed.   If the -e option is given, interpretation of the following backslash-
              escaped characters is enabled.  The -E option disables the interpretation of  these
              escape  characters,  even  on  systems  where they are interpreted by default.  The
              xpg_echo shell option may be used to dynamically  determine  whether  or  not  echo
              expands these escape characters by default.  echo does not interpret -- to mean the
              end of options.  echo interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the eight-bit character whose value is the octal value nnn  (zero  to  three
                     octal digits)
              \xHH   the  eight-bit character whose value is the hexadecimal value HH (one or two
                     hex digits)
              \uHHHH the Unicode (ISO/IEC 10646) character whose value is the  hexadecimal  value
                     HHHH (one to four hex digits)
              \UHHHHHHHH
                     the  Unicode  (ISO/IEC 10646) character whose value is the hexadecimal value
                     HHHHHHHH (one to eight hex digits)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable and disable builtin shell commands.   Disabling  a  builtin  allows  a  disk
              command  which  has  the  same  name  as  a  shell  builtin  to be executed without
              specifying a full pathname, even though the shell normally  searches  for  builtins
              before  disk  commands.  If -n is used, each name is disabled; otherwise, names are
              enabled.  For example, to use the test binary found via the  PATH  instead  of  the
              shell builtin version, run ``enable -n test''.  The -f option means to load the new
              builtin command name from shared object filename, on systems that  support  dynamic
              loading.   The  -d  option  will delete a builtin previously loaded with -f.  If no
              name arguments are given, or if the -p option is supplied, a list of shell builtins
              is printed.  With no other option arguments, the list consists of all enabled shell
              builtins.  If -n is supplied,  only  disabled  builtins  are  printed.   If  -a  is
              supplied,  the list printed includes all builtins, with an indication of whether or
              not each is enabled.  If -s is supplied, the output  is  restricted  to  the  POSIX
              special  builtins.   The  return value is 0 unless a name is not a shell builtin or
              there is an error loading a new builtin from a shared object.

       eval [arg ...]
              The args are read and concatenated together into a single command.  This command is
              then  read  and executed by the shell, and its exit status is returned as the value
              of eval.  If there are no args, or only null arguments, eval returns 0.

       exec [-cl] [-a name] [command [arguments]]
              If command is specified, it replaces the shell.  No new process  is  created.   The
              arguments become the arguments to command.  If the -l option is supplied, the shell
              places a dash at the beginning of the zeroth argument passed to command.   This  is
              what  login(1)  does.   The  -c  option causes command to be executed with an empty
              environment.  If -a is supplied, the shell passes name as the  zeroth  argument  to
              the  executed  command.   If  command  cannot  be  executed for some reason, a non-
              interactive shell exits, unless the execfail shell  option  is  enabled.   In  that
              case,  it returns failure.  An interactive shell returns failure if the file cannot
              be executed.  If command is not specified, any  redirections  take  effect  in  the
              current  shell,  and  the return status is 0.  If there is a redirection error, the
              return status is 1.

       exit [n]
              Cause the shell to exit with a status of n.  If n is omitted, the  exit  status  is
              that  of  the  last  command executed.  A trap on EXIT is executed before the shell
              terminates.

       export [-fn] [name[=word]] ...
       export -p
              The  supplied  names  are  marked  for  automatic  export  to  the  environment  of
              subsequently  executed  commands.   If  the  -f option is given, the names refer to
              functions.  If no names are given, or if the -p option is supplied, a list of names
              of  all exported variables is printed.  The -n option causes the export property to
              be removed from each name.  If a variable name is followed by =word, the  value  of
              the  variable is set to word.  export returns an exit status of 0 unless an invalid
              option is encountered, one of the names is not a valid shell variable name,  or  -f
              is supplied with a name that is not a function.

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              The first form selects a range of commands from first to last from the history list
              and displays or edits and re-executes them.  First and last may be specified  as  a
              string  (to  locate the last command beginning with that string) or as a number (an
              index into the history list, where a negative number is used as an offset from  the
              current command number).  If last is not specified it is set to the current command
              for listing (so that ``fc -l -10'' prints  the  last  10  commands)  and  to  first
              otherwise.  If first is not specified it is set to the previous command for editing
              and -16 for listing.

              The -n option suppresses the command numbers when listing.  The -r option  reverses
              the  order  of the commands.  If the -l option is given, the commands are listed on
              standard output.  Otherwise, the editor  given  by  ename  is  invoked  on  a  file
              containing those commands.  If ename is not given, the value of the FCEDIT variable
              is used, and the value of EDITOR if FCEDIT is not set.  If neither variable is set,
              vi is used.  When editing is complete, the edited commands are echoed and executed.

              In  the  second form, command is re-executed after each instance of pat is replaced
              by rep.  Command is intepreted the same as first above.  A useful alias to use with
              this is ``r="fc -s"'', so that typing ``r cc'' runs the last command beginning with
              ``cc'' and typing ``r'' re-executes the last command.

              If the first form is used, the return value  is  0  unless  an  invalid  option  is
              encountered  or first or last specify history lines out of range.  If the -e option
              is supplied, the return value is the value of the last command executed or  failure
              if  an  error  occurs  with  the temporary file of commands.  If the second form is
              used, the return status is that of the command re-executed,  unless  cmd  does  not
              specify a valid history line, in which case fc returns failure.

       fg [jobspec]
              Resume  jobspec  in the foreground, and make it the current job.  If jobspec is not
              present, the shell's notion of the current job is used.  The return value  is  that
              of  the  command  placed into the foreground, or failure if run when job control is
              disabled or, when run with job control enabled, if jobspec does not specify a valid
              job or jobspec specifies a job that was started without job control.

       getopts optstring name [args]
              getopts  is  used  by  shell  procedures to parse positional parameters.  optstring
              contains the option characters to be recognized; if a character is  followed  by  a
              colon,  the  option is expected to have an argument, which should be separated from
              it by white space.  The colon and question mark  characters  may  not  be  used  as
              option  characters.  Each time it is invoked, getopts places the next option in the
              shell variable name, initializing name if it does not exist, and the index  of  the
              next argument to be processed into the variable OPTIND.  OPTIND is initialized to 1
              each time the shell or a shell script is  invoked.   When  an  option  requires  an
              argument,  getopts  places  that argument into the variable OPTARG.  The shell does
              not reset OPTIND automatically; it must be manually reset between multiple calls to
              getopts within the same shell invocation if a new set of parameters is to be used.

              When  the  end of options is encountered, getopts exits with a return value greater
              than zero.  OPTIND is set to the index of the first non-option argument,  and  name
              is set to ?.

              getopts  normally parses the positional parameters, but if more arguments are given
              in args, getopts parses those instead.

              getopts can report errors in two ways.  If the first character of  optstring  is  a
              colon,  silent  error  reporting is used.  In normal operation, diagnostic messages
              are printed when invalid options or missing option arguments are  encountered.   If
              the  variable  OPTERR is set to 0, no error messages will be displayed, even if the
              first character of optstring is not a colon.

              If an invalid option is seen, getopts places ? into name and, if not silent, prints
              an  error  message  and  unsets OPTARG.  If getopts is silent, the option character
              found is placed in OPTARG and no diagnostic message is printed.

              If a required argument is not found, and getopts is not silent, a question mark (?)
              is  placed  in  name,  OPTARG  is  unset,  and a diagnostic message is printed.  If
              getopts is silent, then a colon (:) is placed in name and  OPTARG  is  set  to  the
              option character found.

              getopts  returns true if an option, specified or unspecified, is found.  It returns
              false if the end of options is encountered or an error occurs.

       hash [-lr] [-p filename] [-dt] [name]
              Each time hash is invoked, the full pathname of the command name is  determined  by
              searching  the  directories  in  $PATH  and  remembered.  Any previously-remembered
              pathname is discarded.  If the -p option is supplied, no path search is  performed,
              and filename is used as the full filename of the command.  The -r option causes the
              shell to forget all remembered locations.  The -d option causes the shell to forget
              the  remembered  location  of  each  name.   If the -t option is supplied, the full
              pathname to which each name corresponds is printed.  If multiple name arguments are
              supplied  with  -t,  the  name  is printed before the hashed full pathname.  The -l
              option causes output to be displayed in a format that may be reused as  input.   If
              no  arguments  are  given,  or if only -l is supplied, information about remembered
              commands is printed.  The return status is true unless a name is not  found  or  an
              invalid option is supplied.

       help [-dms] [pattern]
              Display  helpful information about builtin commands.  If pattern is specified, help
              gives detailed help on all commands matching pattern; otherwise help  for  all  the
              builtins and shell control structures is printed.
              -d     Display a short description of each pattern
              -m     Display the description of each pattern in a manpage-like format
              -s     Display only a short usage synopsis for each pattern

              The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With  no options, display the command history list with line numbers.  Lines listed
              with a * have been modified.  An argument of n lists only the last n lines.  If the
              shell  variable  HISTTIMEFORMAT  is set and not null, it is used as a format string
              for strftime(3) to display the time stamp associated with  each  displayed  history
              entry.   No  intervening  blank is printed between the formatted time stamp and the
              history line.  If filename is supplied, it is used as the name of the history file;
              if  not,  the  value of HISTFILE is used.  Options, if supplied, have the following
              meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.
              -a     Append the ``new'' history lines (history lines entered since the  beginning
                     of the current bash session) to the history file.
              -n     Read  the  history  lines  not  already  read from the history file into the
                     current history list.  These are lines appended to the  history  file  since
                     the beginning of the current bash session.
              -r     Read the contents of the history file and append them to the current history
                     list.
              -w     Write the current history list to the history file, overwriting the  history
                     file's contents.
              -p     Perform history substitution on the following args and display the result on
                     the standard output.  Does not store the results in the history list.   Each
                     arg must be quoted to disable normal history expansion.
              -s     Store  the  args in the history list as a single entry.  The last command in
                     the history list is removed before the args are added.

              If the HISTTIMEFORMAT variable is set, the time stamp information  associated  with
              each  history entry is written to the history file, marked with the history comment
              character.  When the history file is read, lines beginning with the history comment
              character  followed  immediately  by  a digit are interpreted as timestamps for the
              previous history line.   The  return  value  is  0  unless  an  invalid  option  is
              encountered,  an error occurs while reading or writing the history file, an invalid
              offset is supplied as an argument to -d, or the history expansion  supplied  as  an
              argument to -p fails.

       jobs [-lnprs] [ jobspec ... ]
       jobs -x command [ args ... ]
              The first form lists the active jobs.  The options have the following meanings:
              -l     List process IDs in addition to the normal information.
              -n     Display  information only about jobs that have changed status since the user
                     was last notified of their status.
              -p     List only the process ID of the job's process group leader.
              -r     Display only running jobs.
              -s     Display only stopped jobs.

              If jobspec is given, output is restricted  to  information  about  that  job.   The
              return status is 0 unless an invalid option is encountered or an invalid jobspec is
              supplied.

              If the -x option is supplied, jobs replaces any jobspec found in  command  or  args
              with  the  corresponding  process  group  ID, and executes command passing it args,
              returning its exit status.

       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
       kill -l [sigspec | exit_status]
              Send the signal named by sigspec or  signum  to  the  processes  named  by  pid  or
              jobspec.  sigspec is either a case-insensitive signal name such as SIGKILL (with or
              without the SIG prefix) or a signal number; signum is a signal number.  If  sigspec
              is not present, then SIGTERM is assumed.  An argument of -l lists the signal names.
              If any arguments  are  supplied  when  -l  is  given,  the  names  of  the  signals
              corresponding  to  the  arguments  are  listed,  and  the  return status is 0.  The
              exit_status argument to -l is a number specifying either a  signal  number  or  the
              exit status of a process terminated by a signal.  kill returns true if at least one
              signal was successfully sent, or false if an error occurs or an invalid  option  is
              encountered.

       let arg [arg ...]
              Each  arg  is  an  arithmetic expression to be evaluated (see ARITHMETIC EVALUATION
              above).  If the last arg evaluates to 0, let returns 1; 0 is returned otherwise.

       local [option] [name[=value] ...]
              For each argument, a local variable named name is created, and assigned value.  The
              option  can be any of the options accepted by declare.  When local is used within a
              function, it causes the variable name to have a visible scope  restricted  to  that
              function  and  its  children.   With  no  operands,  local  writes  a list of local
              variables to the standard output.  It is an error to use local when  not  within  a
              function.   The  return  status  is  0  unless local is used outside a function, an
              invalid name is supplied, or name is a readonly variable.

       logout Exit a login shell.

       mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
       readarray [-n count] [-O origin] [-s count]  [-t]  [-u  fd]  [-C  callback]  [-c  quantum]
       [array]
              Read  lines  from the standard input into the indexed array variable array, or from
              file descriptor fd if the -u option is  supplied.   The  variable  MAPFILE  is  the
              default array.  Options, if supplied, have the following meanings:
              -n     Copy at most count lines.  If count is 0, all lines are copied.
              -O     Begin assigning to array at index origin.  The default index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing newline from each line read.
              -u     Read lines from file descriptor fd instead of the standard input.
              -C     Evaluate callback each time quantum lines are read.  The -c option specifies
                     quantum.
              -c     Specify the number of lines read between each call to callback.

              If -C is specified without -c, the default  quantum  is  5000.   When  callback  is
              evaluated,  it  is  supplied the index of the next array element to be assigned and
              the line to be assigned to that  element  as  additional  arguments.   callback  is
              evaluated after the line is read but before the array element is assigned.

              If  not supplied with an explicit origin, mapfile will clear array before assigning
              to it.

              mapfile returns successfully  unless  an  invalid  option  or  option  argument  is
              supplied, array is invalid or unassignable, or if array is not an indexed array.

       popd [-n] [+n] [-n]
              Removes  entries  from  the  directory  stack.   With no arguments, removes the top
              directory from the stack, and performs a cd to the new top  directory.   Arguments,
              if supplied, have the following meanings:
              -n     Suppresses the normal change of directory when removing directories from the
                     stack, so that only the stack is manipulated.
              +n     Removes the nth entry counting from the left of  the  list  shown  by  dirs,
                     starting  with  zero.  For example: ``popd +0'' removes the first directory,
                     ``popd +1'' the second.
              -n     Removes the nth entry counting from the right of the  list  shown  by  dirs,
                     starting  with  zero.   For example: ``popd -0'' removes the last directory,
                     ``popd -1'' the next to last.

              If the popd command is successful, a dirs is performed  as  well,  and  the  return
              status is 0.  popd returns false if an invalid option is encountered, the directory
              stack is empty, a non-existent directory stack entry is specified, or the directory
              change fails.

       printf [-v var] format [arguments]
              Write  the  formatted  arguments  to  the  standard output under the control of the
              format.  The -v option causes the output to be assigned to the variable var  rather
              than being printed to the standard output.

              The  format  is  a  character  string  which contains three types of objects: plain
              characters, which are simply copied to standard output, character escape sequences,
              which  are  converted and copied to the standard output, and format specifications,
              each of which causes printing of the next successive argument.  In addition to  the
              standard   printf(1)   format   specifications,  printf  interprets  the  following
              extensions:
              %b     causes printf to expand backslash  escape  sequences  in  the  corresponding
                     argument  (except  that  \c terminates output, backslashes in \', \", and \?
                     are not removed, and octal escapes beginning with \0 may contain up to  four
                     digits).
              %q     causes  printf  to output the corresponding argument in a format that can be
                     reused as shell input.
              %(datefmt)T
                     causes printf to output the date-time string resulting from using datefmt as
                     a  format  string for strftime(3).  The corresponding argument is an integer
                     representing the number of seconds since the epoch.   Two  special  argument
                     values  may  be  used: -1 represents the current time, and -2 represents the
                     time the shell was invoked.  If no argument is specified, conversion behaves
                     as if -1 had been given.  This is an exception to the usual printf behavior.

              Arguments to non-string format specifiers are treated as C constants, except that a
              leading plus or minus sign is allowed, and if the leading character is a single  or
              double quote, the value is the ASCII value of the following character.

              The  format  is reused as necessary to consume all of the arguments.  If the format
              requires more arguments than are supplied, the extra format  specifications  behave
              as  if  a zero value or null string, as appropriate, had been supplied.  The return
              value is zero on success, non-zero on failure.

       pushd [-n] [+n] [-n]
       pushd [-n] [dir]
              Adds a directory to the top of the directory stack, or rotates  the  stack,  making
              the  new  top  of  the  stack  the  current  working directory.  With no arguments,
              exchanges the top two directories and returns 0,  unless  the  directory  stack  is
              empty.  Arguments, if supplied, have the following meanings:
              -n     Suppresses  the  normal  change  of directory when adding directories to the
                     stack, so that only the stack is manipulated.
              +n     Rotates the stack so that the nth directory (counting from the left  of  the
                     list shown by dirs, starting with zero) is at the top.
              -n     Rotates  the stack so that the nth directory (counting from the right of the
                     list shown by dirs, starting with zero) is at the top.
              dir    Adds dir to the directory stack at  the  top,  making  it  the  new  current
                     working  directory  as  if  it  had  been supplied as the argument to the cd
                     builtin.

              If the pushd command is successful, a dirs is performed as well.  If the first form
              is  used,  pushd returns 0 unless the cd to dir fails.  With the second form, pushd
              returns 0 unless the directory stack  is  empty,  a  non-existent  directory  stack
              element  is  specified,  or  the  directory  change  to  the  specified new current
              directory fails.

       pwd [-LP]
              Print the absolute pathname of the current working directory.  The pathname printed
              contains  no  symbolic links if the -P option is supplied or the -o physical option
              to the set builtin command is enabled.  If the -L  option  is  used,  the  pathname
              printed  may contain symbolic links.  The return status is 0 unless an error occurs
              while reading the name of the current directory or an invalid option is supplied.

       read [-ers] [-a aname] [-d delim] [-i text]  [-n  nchars]  [-N  nchars]  [-p  prompt]  [-t
       timeout] [-u fd] [name ...]
              One  line  is read from the standard input, or from the file descriptor fd supplied
              as an argument to the -u option, and the first word is assigned to the first  name,
              the  second  word  to  the  second  name,  and so on, with leftover words and their
              intervening separators assigned to the last name.  If there are  fewer  words  read
              from  the  input  stream than names, the remaining names are assigned empty values.
              The characters in IFS are used to split the line into words using  the  same  rules
              the shell uses for expansion (described above under Word Splitting).  The backslash
              character (\) may be used to remove any special meaning for the next character read
              and for line continuation.  Options, if supplied, have the following meanings:
              -a aname
                     The  words  are  assigned to sequential indices of the array variable aname,
                     starting at 0.  aname is unset before any new values  are  assigned.   Other
                     name arguments are ignored.
              -d delim
                     The  first  character  of  delim is used to terminate the input line, rather
                     than newline.
              -e     If the standard input is coming from  a  terminal,  readline  (see  READLINE
                     above)  is  used to obtain the line.  Readline uses the current (or default,
                     if line editing was not previously active) editing settings.
              -i text
                     If readline is being used to read the line, text is placed into the  editing
                     buffer before editing begins.
              -n nchars
                     read  returns  after  reading  nchars  characters  rather than waiting for a
                     complete line  of  input,  but  honor  a  delimiter  if  fewer  than  nchars
                     characters are read before the delimiter.
              -N nchars
                     read returns after reading exactly nchars characters rather than waiting for
                     a complete line of input, unless EOF  is  encountered  or  read  times  out.
                     Delimiter  characters encountered in the input are not treated specially and
                     do not cause read to return until nchars characters are read.
              -p prompt
                     Display prompt  on  standard  error,  without  a  trailing  newline,  before
                     attempting  to  read  any  input.   The prompt is displayed only if input is
                     coming from a terminal.
              -r     Backslash does not act as an escape character.  The backslash is  considered
                     to  be part of the line.  In particular, a backslash-newline pair may not be
                     used as a line continuation.
              -s     Silent mode.  If input is coming from a terminal, characters are not echoed.
              -t timeout
                     Cause read to time out and return failure if a complete line of input (or  a
                     specified number of characters) is not read within timeout seconds.  timeout
                     may be a decimal number with a  fractional  portion  following  the  decimal
                     point.   This  option  is  only  effective  if  read is reading input from a
                     terminal, pipe, or other special file; it has no effect  when  reading  from
                     regular  files.   If  read times out, read saves any partial input read into
                     the specified variable name.  If timeout is  0,  read  returns  immediately,
                     without trying to read any data.  The exit status is 0 if input is available
                     on the specified file descriptor, non-zero otherwise.  The  exit  status  is
                     greater than 128 if the timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If  no  names  are  supplied, the line read is assigned to the variable REPLY.  The
              return code is zero, unless end-of-file is encountered, read times  out  (in  which
              case  the  return  code  is greater than 128), a variable assignment error (such as
              assigning to a readonly variable) occurs, or an invalid file descriptor is supplied
              as the argument to -u.

       readonly [-aAf] [-p] [name[=word] ...]
              The  given  names are marked readonly; the values of these names may not be changed
              by  subsequent  assignment.   If  the  -f  option  is   supplied,   the   functions
              corresponding to the names are so marked.  The -a option restricts the variables to
              indexed arrays; the -A option restricts the variables to  associative  arrays.   If
              both options are supplied, -A takes precedence.  If no name arguments are given, or
              if the -p option is supplied, a list of all readonly names is printed.   The  other
              options  may  be  used  to  restrict  the output to a subset of the set of readonly
              names.  The -p option causes output to be displayed in a format that may be  reused
              as  input.   If  a variable name is followed by =word, the value of the variable is
              set to word.  The return status is 0 unless an invalid option is  encountered,  one
              of the names is not a valid shell variable name, or -f is supplied with a name that
              is not a function.

       return [n]
              Causes a function to stop executing and return the value  specified  by  n  to  its
              caller.  If n is omitted, the return status is that of the last command executed in
              the function body.  If return is used outside a function, but during execution of a
              script  by  the  .   (source)  command,  it causes the shell to stop executing that
              script and return either n or the exit status of the last command  executed  within
              the script as the exit status of the script.  If n is supplied, the return value is
              its least significant 8 bits.  The return status is non-zero if return is  supplied
              a non-numeric argument, or is used outside a function and not during execution of a
              script by . or source.  Any command associated with the  RETURN  trap  is  executed
              before execution resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
              Without  options,  the  name  and  value  of each shell variable are displayed in a
              format that can be reused as input  for  setting  or  resetting  the  currently-set
              variables.   Read-only  variables  cannot  be  reset.   In  posix  mode, only shell
              variables are listed.  The output is sorted according to the current locale.   When
              options are specified, they set or unset shell attributes.  Any arguments remaining
              after option processing are treated as values for the positional parameters and are
              assigned,  in order, to $1, $2, ...  $n.  Options, if specified, have the following
              meanings:
              -a      Automatically mark variables and functions which are  modified  or  created
                      for export to the environment of subsequent commands.
              -b      Report  the  status  of terminated background jobs immediately, rather than
                      before the next primary prompt.  This is effective only when job control is
                      enabled.
              -e      Exit  immediately  if  a  pipeline  (which  may  consist of a single simple
                      command), a list, or a compound command (see SHELL GRAMMAR  above),   exits
                      with  a non-zero status.  The shell does not exit if the command that fails
                      is part of the command list immediately following a while or until keyword,
                      part  of  the  test  following  the  if or elif reserved words, part of any
                      command executed in a && or || list except the command following the  final
                      &&  or  ||,  any  command  in  a pipeline but the last, or if the command's
                      return value is being inverted with !.  If a compound command other than  a
                      subshell  returns  a  non-zero status because a command failed while -e was
                      being ignored, the shell does not exit.  A trap on ERR, if set, is executed
                      before  the  shell exits.  This option applies to the shell environment and
                      each subshell environment separately  (see  COMMAND  EXECUTION  ENVIRONMENT
                      above),  and  may cause subshells to exit before executing all the commands
                      in the subshell.

                      If a compound command or shell function executes in a context where  -e  is
                      being ignored, none of the commands executed within the compound command or
                      function body will be affected by the -e setting, even if -e is set  and  a
                      command  returns a failure status.  If a compound command or shell function
                      sets -e while executing in a context where -e is ignored, that setting will
                      not  have  any  effect until the compound command or the command containing
                      the function call completes.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they  are  looked  up  for  execution.
                      This is enabled by default.
              -k      All  arguments  in  the  form  of  assignment  statements are placed in the
                      environment for a command, not just those that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This option is on  by  default  for
                      interactive shells on systems that support it (see JOB CONTROL above).  All
                      processes  run  in  a  separate  process  group.   When  a  background  job
                      completes, the shell prints a line containing its exit status.
              -n      Read  commands  but do not execute them.  This may be used to check a shell
                      script for syntax errors.  This is ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use an emacs-style command line editing interface.  This is enabled
                              by  default  when  the  shell  is  interactive, unless the shell is
                              started with the --noediting option.  This also affects the editing
                              interface used for read -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable  command  history,  as  described above under HISTORY.  This
                              option is on by default in interactive shells.
                      ignoreeof
                              The effect is as if the shell  command  ``IGNOREEOF=10''  had  been
                              executed (see Shell Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If  set,  the  return  value of a pipeline is the value of the last
                              (rightmost) command to exit with a non-zero status, or zero if  all
                              commands  in  the  pipeline  exit  successfully.   This  option  is
                              disabled by default.
                      posix   Change the behavior of bash where  the  default  operation  differs
                              from  the  POSIX  standard to match the standard (posix mode).  See
                              SEE ALSO below for a reference to a document that details how posix
                              mode affects bash's behavior.
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use  a  vi-style command line editing interface.  This also affects
                              the editing interface used for read -e.
                      xtrace  Same as -x.
                      If -o is supplied with no option-name, the values of  the  current  options
                      are  printed.   If  +o  is  supplied  with  no option-name, a series of set
                      commands to recreate the  current  option  settings  is  displayed  on  the
                      standard output.
              -p      Turn  on  privileged  mode.  In this mode, the $ENV and $BASH_ENV files are
                      not processed, shell functions are not inherited from the environment,  and
                      the  SHELLOPTS,  BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear
                      in the environment,  are  ignored.   If  the  shell  is  started  with  the
                      effective user (group) id not equal to the real user (group) id, and the -p
                      option is not supplied, these actions are taken and the effective  user  id
                      is  set  to the real user id.  If the -p option is supplied at startup, the
                      effective user id is  not  reset.   Turning  this  option  off  causes  the
                      effective user and group ids to be set to the real user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat  unset variables and parameters other than the special parameters "@"
                      and "*" as an error when performing parameter expansion.  If  expansion  is
                      attempted  on  an  unset  variable  or parameter, the shell prints an error
                      message, and, if not interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After expanding each simple command,  for  command,  case  command,  select
                      command,  or  arithmetic  for  command,  display the expanded value of PS4,
                      followed by the command and its expanded arguments or associated word list.
              -B      The shell performs brace expansion (see Brace Expansion above).  This is on
                      by default.
              -C      If  set,  bash  does  not overwrite an existing file with the >, >&, and <>
                      redirection operators.  This may be overridden when creating  output  files
                      by using the redirection operator >| instead of >.
              -E      If  set,  any  trap  on  ERR  is  inherited  by  shell  functions,  command
                      substitutions, and commands executed in a subshell  environment.   The  ERR
                      trap is normally not inherited in such cases.
              -H      Enable  !   style  history substitution.  This option is on by default when
                      the shell is interactive.
              -P      If set, the shell does not resolve symbolic links when  executing  commands
                      such as cd that change the current working directory.  It uses the physical
                      directory structure instead.  By default, bash follows the logical chain of
                      directories when performing commands which change the current directory.
              -T      If  set,  any  traps  on DEBUG and RETURN are inherited by shell functions,
                      command substitutions, and commands executed  in  a  subshell  environment.
                      The DEBUG and RETURN traps are normally not inherited in such cases.
              --      If  no  arguments  follow  this  option, then the positional parameters are
                      unset.  Otherwise, the positional parameters are set to the args,  even  if
                      some of them begin with a -.
              -       Signal  the  end of options, cause all remaining args to be assigned to the
                      positional parameters.  The -x and -v options are turned off.  If there are
                      no args, the positional parameters remain unchanged.

              The  options  are  off  by  default  unless otherwise noted.  Using + rather than -
              causes these options to be turned off.   The  options  can  also  be  specified  as
              arguments  to  an invocation of the shell.  The current set of options may be found
              in $-.  The return status is always true unless an invalid option is encountered.

       shift [n]
              The positional  parameters  from  n+1  ...  are  renamed  to  $1  ....   Parameters
              represented  by  the numbers $# down to $#-n+1 are unset.  n must be a non-negative
              number less than or equal to $#.  If n is 0, no parameters are changed.   If  n  is
              not  given,  it  is  assumed  to  be  1.   If  n is greater than $#, the positional
              parameters are not changed.  The return status is greater than zero if n is greater
              than $# or less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
              Toggle  the  values  of settings controlling optional shell behavior.  The settings
              can be either those listed below, or, if the -o option  is  used,  those  available
              with  the  -o  option  to the set builtin command.  With no options, or with the -p
              option, a list of all settable options is displayed, with an indication of  whether
              or not each is set.  The -p option causes output to be displayed in a form that may
              be reused as input.  Other options have the following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses normal output (quiet mode); the return status  indicates  whether
                     the  optname  is set or unset.  If multiple optname arguments are given with
                     -q, the return  status  is  zero  if  all  optnames  are  enabled;  non-zero
                     otherwise.
              -o     Restricts the values of optname to be those defined for the -o option to the
                     set builtin.

              If either -s or -u is used with  no  optname  arguments,  shopt  shows  only  those
              options  which  are  set or unset, respectively.  Unless otherwise noted, the shopt
              options are disabled (unset) by default.

              The return status when listing options is zero if all optnames  are  enabled,  non-
              zero  otherwise.   When  setting  or  unsetting  options, the return status is zero
              unless an optname is not a valid shell option.

              The list of shopt options is:

              autocd  If set, a command name that is the name of a directory is executed as if it
                      were  the  argument  to  the  cd  command.   This  option  is  only used by
                      interactive shells.
              cdable_vars
                      If set, an argument to the cd builtin command that is not  a  directory  is
                      assumed to be the name of a variable whose value is the directory to change
                      to.
              cdspell If set, minor errors in the spelling of  a  directory  component  in  a  cd
                      command   will  be  corrected.   The  errors  checked  for  are  transposed
                      characters, a  missing  character,  and  one  character  too  many.   If  a
                      correction  is  found,  the  corrected filename is printed, and the command
                      proceeds.  This option is only used by interactive shells.
              checkhash
                      If set, bash checks that a command found in the hash  table  exists  before
                      trying  to execute it.  If a hashed command no longer exists, a normal path
                      search is performed.
              checkjobs
                      If set, bash lists the status  of  any  stopped  and  running  jobs  before
                      exiting  an  interactive  shell.   If any jobs are running, this causes the
                      exit to be deferred until a second exit is attempted without an intervening
                      command (see JOB CONTROL above).  The shell always postpones exiting if any
                      jobs are stopped.
              checkwinsize
                      If set, bash checks the window size after each command and,  if  necessary,
                      updates the values of LINES and COLUMNS.
              cmdhist If  set,  bash attempts to save all lines of a multiple-line command in the
                      same history entry.  This allows easy re-editing of multi-line commands.
              compat31
                      If set, bash changes its behavior to that of version 3.1  with  respect  to
                      quoted  arguments  to  the [[ conditional command's =~ operator and locale-
                      specific string comparison when using the [[ conditional command's < and  >
                      operators.   Bash  versions  prior  to  bash-4.1  use  ASCII  collation and
                      strcmp(3); bash-4.1 and later use the current locale's  collation  sequence
                      and strcoll(3).
              compat32
                      If  set,  bash  changes its behavior to that of version 3.2 with respect to
                      locale-specific string comparison when using the [[ conditional command's <
                      and > operators (see previous item).
              compat40
                      If  set,  bash  changes its behavior to that of version 4.0 with respect to
                      locale-specific string comparison when using the [[ conditional command's <
                      and   >   operators  (see  description  of  compat31)  and  the  effect  of
                      interrupting a command list.  Bash versions 4.0  and  later  interrupt  the
                      list  as  if  the  shell received the interrupt; previous versions continue
                      with the next command in the list.
              compat41
                      If set, bash, when in posix mode, treats a single quote in a  double-quoted
                      parameter  expansion  as a special character.  The single quotes must match
                      (an  even  number)  and  the  characters  between  the  single  quotes  are
                      considered quoted.  This is the behavior of posix mode through version 4.1.
                      The default bash behavior remains as in previous versions.
              compat42
                      If set, bash does  not  process  the  replacement  string  in  the  pattern
                      substitution word expansion using quote removal.
              complete_fullquote
                      If  set,  bash  quotes  all shell metacharacters in filenames and directory
                      names when performing completion.  If not set, bash removes  metacharacters
                      such  as  the dollar sign from the set of characters that will be quoted in
                      completed filenames when these  metacharacters  appear  in  shell  variable
                      references  in  words  to  be  completed.   This means that dollar signs in
                      variable names that expand to directories will not be quoted; however,  any
                      dollar  signs  appearing  in filenames will not be quoted, either.  This is
                      active only when bash is using backslashes to  quote  completed  filenames.
                      This  variable  is  set  by  default, which is the default bash behavior in
                      versions through 4.2.
              direxpand
                      If set, bash replaces directory names with the results  of  word  expansion
                      when  performing  filename  completion.   This  changes the contents of the
                      readline editing buffer.  If not set, bash attempts to  preserve  what  the
                      user typed.
              dirspell
                      If  set,  bash  attempts spelling correction on directory names during word
                      completion if the directory name initially supplied does not exist.
              dotglob If set, bash includes filenames beginning with a  `.'  in  the  results  of
                      pathname expansion.
              execfail
                      If set, a non-interactive shell will not exit if it cannot execute the file
                      specified as an argument to the exec builtin command.  An interactive shell
                      does not exit if exec fails.
              expand_aliases
                      If set, aliases are expanded as described above under ALIASES.  This option
                      is enabled by default for interactive shells.
              extdebug
                      If set, behavior intended for use by debuggers is enabled:
                      1.     The -F option to the declare builtin displays the source  file  name
                             and  line  number corresponding to each function name supplied as an
                             argument.
                      2.     If the command run by the DEBUG trap returns a non-zero  value,  the
                             next command is skipped and not executed.
                      3.     If  the  command run by the DEBUG trap returns a value of 2, and the
                             shell is executing in a subroutine (a  shell  function  or  a  shell
                             script  executed  by  the . or source builtins), a call to return is
                             simulated.
                      4.     BASH_ARGC  and  BASH_ARGV  are  updated  as   described   in   their
                             descriptions above.
                      5.     Function tracing is enabled:  command substitution, shell functions,
                             and subshells invoked with ( command ) inherit the DEBUG and  RETURN
                             traps.
                      6.     Error  tracing  is  enabled:  command substitution, shell functions,
                             and subshells invoked with ( command ) inherit the ERR trap.
              extglob If set, the  extended  pattern  matching  features  described  above  under
                      Pathname Expansion are enabled.
              extquote
                      If  set,  $'string'  and $"string" quoting is performed within ${parameter}
                      expansions enclosed in double quotes.  This option is enabled by default.
              failglob
                      If set, patterns which fail to match filenames  during  pathname  expansion
                      result in an expansion error.
              force_fignore
                      If set, the suffixes specified by the FIGNORE shell variable cause words to
                      be ignored when performing word completion even if the  ignored  words  are
                      the only possible completions.  See SHELL VARIABLES above for a description
                      of FIGNORE.  This option is enabled by default.
              globasciiranges
                      If set, range expressions used in pattern matching bracket expressions (see
                      Pattern  Matching  above)  behave  as  if  in the traditional C locale when
                      performing comparisons.  That is, the current locale's  collating  sequence
                      is  not  taken  into  account,  so  b will not collate between A and B, and
                      upper-case and lower-case ASCII characters will collate together.
              globstar
                      If set, the pattern ** used in a pathname expansion context will match  all
                      files  and  zero or more directories and subdirectories.  If the pattern is
                      followed by a /, only directories and subdirectories match.
              gnu_errfmt
                      If set, shell error messages are written in the standard GNU error  message
                      format.
              histappend
                      If  set, the history list is appended to the file named by the value of the
                      HISTFILE variable when the shell exits, rather than overwriting the file.
              histreedit
                      If set, and readline is being used, a user is given the opportunity to  re-
                      edit a failed history substitution.
              histverify
                      If set, and readline is being used, the results of history substitution are
                      not immediately passed to the shell parser.  Instead, the resulting line is
                      loaded into the readline editing buffer, allowing further modification.
              hostcomplete
                      If  set,  and readline is being used, bash will attempt to perform hostname
                      completion when a word containing a @ is being  completed  (see  Completing
                      under READLINE above).  This is enabled by default.
              huponexit
                      If  set,  bash will send SIGHUP to all jobs when an interactive login shell
                      exits.
              interactive_comments
                      If set, allow a word beginning with # to cause that word and all  remaining
                      characters on that line to be ignored in an interactive shell (see COMMENTS
                      above).  This option is enabled by default.
              lastpipe
                      If set, and job control is not active, the shell runs the last command of a
                      pipeline not executed in the background in the current shell environment.
              lithist If set, and the cmdhist option is enabled, multi-line commands are saved to
                      the history with embedded newlines rather than using  semicolon  separators
                      where possible.
              login_shell
                      The  shell  sets  this  option  if  it  is  started  as  a login shell (see
                      INVOCATION above).  The value may not be changed.
              mailwarn
                      If set, and a file that bash is checking for mail has been  accessed  since
                      the  last  time it was checked, the message ``The mail in mailfile has been
                      read'' is displayed.
              no_empty_cmd_completion
                      If set, and readline is being used, bash will not  attempt  to  search  the
                      PATH  for  possible  completions  when  completion is attempted on an empty
                      line.
              nocaseglob
                      If  set,  bash  matches  filenames  in  a  case-insensitive  fashion   when
                      performing pathname expansion (see Pathname Expansion above).
              nocasematch
                      If set, bash matches patterns in a case-insensitive fashion when performing
                      matching while executing case or [[ conditional commands.
              nullglob
                      If set, bash allows patterns which match no files (see  Pathname  Expansion
                      above) to expand to a null string, rather than themselves.
              progcomp
                      If set, the programmable completion facilities (see Programmable Completion
                      above) are enabled.  This option is enabled by default.
              promptvars
                      If set, prompt strings undergo parameter expansion,  command  substitution,
                      arithmetic  expansion,  and quote removal after being expanded as described
                      in PROMPTING above.  This option is enabled by default.
              restricted_shell
                      The shell sets this option  if  it  is  started  in  restricted  mode  (see
                      RESTRICTED  SHELL below).  The value may not be changed.  This is not reset
                      when the startup files are executed, allowing the startup files to discover
                      whether or not a shell is restricted.
              shift_verbose
                      If  set,  the  shift  builtin  prints an error message when the shift count
                      exceeds the number of positional parameters.
              sourcepath
                      If set, the source (.) builtin uses the value of PATH to find the directory
                      containing  the  file  supplied  as an argument.  This option is enabled by
                      default.
              xpg_echo
                      If set, the echo builtin expands backslash-escape sequences by default.

       suspend [-f]
              Suspend the execution of this shell until it receives a SIGCONT  signal.   A  login
              shell cannot be suspended; the -f option can be used to override this and force the
              suspension.  The return status is 0 unless the shell is a login shell and -f is not
              supplied, or if job control is not enabled.

       test expr
       [ expr ]
              Return  a  status  of  0  (true)  or  1  (false) depending on the evaluation of the
              conditional expression  expr.   Each  operator  and  operand  must  be  a  separate
              argument.   Expressions  are  composed  of  the  primaries  described  above  under
              CONDITIONAL EXPRESSIONS.  test does not accept any options, nor does it accept  and
              ignore an argument of -- as signifying the end of options.

              Expressions  may  be  combined  using the following operators, listed in decreasing
              order of precedence.  The evaluation depends on the number of arguments; see below.
              Operator precedence is used when there are five or more arguments.
              ! expr True if expr is false.
              ( expr )
                     Returns  the  value  of  expr.   This  may  be  used  to override the normal
                     precedence of operators.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

              test and [ evaluate conditional expressions using a  set  of  rules  based  on  the
              number of arguments.

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not null.
              2 arguments
                     If the first argument is !, the expression is true if and only if the second
                     argument is null.  If the first argument is one  of  the  unary  conditional
                     operators listed above under CONDITIONAL EXPRESSIONS, the expression is true
                     if the unary test is true.  If the first  argument  is  not  a  valid  unary
                     conditional operator, the expression is false.
              3 arguments
                     The  following  conditions  are  applied in the order listed.  If the second
                     argument is one of the  binary  conditional  operators  listed  above  under
                     CONDITIONAL  EXPRESSIONS,  the result of the expression is the result of the
                     binary test using the first and third arguments as operands.  The -a and  -o
                     operators  are  considered  binary operators when there are three arguments.
                     If the first argument is !, the value is the negation  of  the  two-argument
                     test using the second and third arguments.  If the first argument is exactly
                     ( and the third argument is exactly ), the result is the  one-argument  test
                     of the second argument.  Otherwise, the expression is false.
              4 arguments
                     If the first argument is !, the result is the negation of the three-argument
                     expression composed of the remaining arguments.  Otherwise,  the  expression
                     is  parsed  and  evaluated  according  to  precedence using the rules listed
                     above.
              5 or more arguments
                     The expression is parsed and evaluated according  to  precedence  using  the
                     rules listed above.

              When  used with test or [, the < and > operators sort lexicographically using ASCII
              ordering.

       times  Print the accumulated user and system times for the shell  and  for  processes  run
              from the shell.  The return status is 0.

       trap [-lp] [[arg] sigspec ...]
              The  command  arg  is  to  be  read  and executed when the shell receives signal(s)
              sigspec.  If arg is absent (and there is a single sigspec)  or  -,  each  specified
              signal  is reset to its original disposition (the value it had upon entrance to the
              shell).  If arg is the null string the signal specified by each sigspec is  ignored
              by the shell and by the commands it invokes.  If arg is not present and -p has been
              supplied, then the trap commands associated with each sigspec are displayed.  If no
              arguments  are  supplied  or  if only -p is given, trap prints the list of commands
              associated with each signal.  The -l option causes the shell to  print  a  list  of
              signal names and their corresponding numbers.  Each sigspec is either a signal name
              defined in <signal.h>, or a signal number.  Signal names are case  insensitive  and
              the SIG prefix is optional.

              If  a sigspec is EXIT (0) the command arg is executed on exit from the shell.  If a
              sigspec is DEBUG, the command arg is executed  before  every  simple  command,  for
              command, case command, select command, every arithmetic for command, and before the
              first command executes in a shell function (see SHELL GRAMMAR above).  Refer to the
              description  of  the extdebug option to the shopt builtin for details of its effect
              on the DEBUG trap.  If a sigspec is RETURN, the command arg is executed each time a
              shell  function  or  a  script  executed  with  the  .  or source builtins finishes
              executing.

              If a sigspec is ERR, the command arg is executed whenever a a pipeline  (which  may
              consist  of  a  single  simple  command),  a  list, or a compound command returns a
              non-zero exit status, subject to the following conditions.  The  ERR  trap  is  not
              executed  if the failed command is part of the command list immediately following a
              while or until keyword, part of the test in an if  statement,  part  of  a  command
              executed  in  a  && or || list except the command following the final && or ||, any
              command in a pipeline but the last, or if  the  command's  return  value  is  being
              inverted using !.  These are the same conditions obeyed by the errexit (-e) option.

              Signals  ignored  upon  entry  to  the  shell  cannot be trapped or reset.  Trapped
              signals that are not being ignored are reset to their original values in a subshell
              or  subshell  environment  when  one is created.  The return status is false if any
              sigspec is invalid; otherwise trap returns true.

       type [-aftpP] name [name ...]
              With no options, indicate how each name would be interpreted if used as  a  command
              name.   If  the  -t  option  is  used,  type prints a string which is one of alias,
              keyword, function, builtin, or file if name  is  an  alias,  shell  reserved  word,
              function,  builtin,  or  disk  file,  respectively.  If the name is not found, then
              nothing is printed, and an exit status of false is returned.  If the -p  option  is
              used,  type either returns the name of the disk file that would be executed if name
              were specified as a command name, or nothing if ``type -t name'' would  not  return
              file.   The  -P option forces a PATH search for each name, even if ``type -t name''
              would not return file.  If a command is hashed, -p and -P print the  hashed  value,
              which  is not necessarily the file that appears first in PATH.  If the -a option is
              used, type prints all of the places that contain an executable  named  name.   This
              includes aliases and functions, if and only if the -p option is not also used.  The
              table of hashed commands is not consulted when using -a.  The -f option  suppresses
              shell  function  lookup,  as with the command builtin.  type returns true if all of
              the arguments are found, false if any are not found.

       ulimit [-HSTabcdefilmnpqrstuvx [limit]]
              Provides control over the resources available to the shell and to processes started
              by  it, on systems that allow such control.  The -H and -S options specify that the
              hard or soft limit is set for the given resource.  A hard limit cannot be increased
              by a non-root user once it is set; a soft limit may be increased up to the value of
              the hard limit.  If neither -H nor -S is specified, both the soft and  hard  limits
              are set.  The value of limit can be a number in the unit specified for the resource
              or one of the special values hard, soft, or unlimited, which stand for the  current
              hard  limit,  the  current  soft  limit,  and  no limit, respectively.  If limit is
              omitted, the current value of the soft limit of the resource is printed, unless the
              -H  option  is given.  When more than one resource is specified, the limit name and
              unit are printed before the value.  Other options are interpreted as follows:
              -a     All current limits are reported
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The maximum size of files written by the shell and its children
              -i     The maximum number of pending signals
              -l     The maximum size that may be locked into memory
              -m     The maximum resident set size (many systems do not honor this limit)
              -n     The maximum number of open file descriptors (most systems do not allow  this
                     value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The maximum number of processes available to a single user
              -v     The  maximum  amount  of  virtual memory available to the shell and, on some
                     systems, to its children
              -x     The maximum number of file locks
              -T     The maximum number of threads

              If limit is given, and the -a option is not used, limit is the  new  value  of  the
              specified  resource.   If  no  option  is given, then -f is assumed.  Values are in
              1024-byte increments, except for -t, which is in seconds; -p, which is in units  of
              512-byte  blocks;  and  -T,  -b, -n, and -u, which are unscaled values.  The return
              status is 0 unless an invalid option or argument is supplied, or  an  error  occurs
              while setting a new limit.

       umask [-p] [-S] [mode]
              The  user  file-creation  mask  is set to mode.  If mode begins with a digit, it is
              interpreted as an octal number; otherwise it is interpreted as a symbolic mode mask
              similar to that accepted by chmod(1).  If mode is omitted, the current value of the
              mask is printed.  The -S option causes the mask to be printed in symbolic form; the
              default  output  is  an  octal  number.   If the -p option is supplied, and mode is
              omitted, the output is in a form that may be reused as input.  The return status is
              0  if  the  mode  was successfully changed or if no mode argument was supplied, and
              false otherwise.

       unalias [-a] [name ...]
              Remove each name from the list of defined aliases.  If -a is  supplied,  all  alias
              definitions  are removed.  The return value is true unless a supplied name is not a
              defined alias.

       unset [-fv] [-n] [name ...]
              For each name, remove the corresponding variable or function.  If the -v option  is
              given,  each  name refers to a shell variable, and that variable is removed.  Read-
              only variables may not be unset.  If -f is specified, each name refers to  a  shell
              function,  and  the  function definition is removed.  If the -n option is supplied,
              and name is a variable with the nameref attribute, name will be unset  rather  than
              the  variable it references.  -n has no effect if the -f option is supplied.  If no
              options are supplied, each name refers to a variable; if there is  no  variable  by
              that  name,  any function with that name is unset.  Each unset variable or function
              is removed  from  the  environment  passed  to  subsequent  commands.   If  any  of
              COMP_WORDBREAKS,  RANDOM,  SECONDS,  LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK
              are unset, they lose their special properties, even if they are subsequently reset.
              The exit status is true unless a name is readonly.

       wait [-n] [n ...]
              Wait  for  each  specified child process and return its termination status.  Each n
              may be a process ID or a job specification; if a job spec is given,  all  processes
              in  that  job's  pipeline  are waited for.  If n is not given, all currently active
              child processes are waited for, and the return status is zero.  If the -n option is
              supplied,  wait  waits  for any job to terminate and returns its exit status.  If n
              specifies a non-existent process or job, the return status is 127.  Otherwise,  the
              return status is the exit status of the last process or job waited for.

SEE ALSO

       bash(1), sh(1)